Transparent conductors are widely used in the flat-panel display industry to form electrodes for electrically switching the light-emitting or light-transmitting properties of a display pixel, for example in liquid crystal or organic light-emitting diode displays. Transparent conductive electrodes are also used in touch screens in conjunction with displays. In such applications, the transparency and conductivity of the transparent electrodes are important attributes. In general, it is desired that transparent conductors have a high transparency (for example, greater than 90% in the visible spectrum) and a low electrical resistivity (for example, less than 10 ohms/square).
Touch screens with transparent electrodes are widely used with electronic displays, especially for mobile electronic devices. Such devices typically include a touch screen mounted over an electronic display that displays interactive information. Touch screens mounted over a display device are largely transparent so a user can view displayed information through the touch-screen and readily locate a point on the touch-screen to touch and thereby indicate the information relevant to the touch. By physically touching, or nearly touching, the touch screen in a location associated with particular information, a user can indicate an interest, selection, or desired manipulation of the associated particular information. The touch screen detects the touch and then electronically interacts with a processor to indicate the touch and touch location. The processor can then associate the touch and touch location with displayed information to execute a programmed task associated with the information. For example, graphic elements in a computer-driven graphic user interface are selected or manipulated with a touch screen mounted on a display that displays the graphic user interface.
Referring to FIG. 10, a prior-art display and touch-screen system 100 includes a display 110 having a display area 111. A corresponding touch screen 120 is mounted with display 110 so that information displayed on display 110 in display area 111 can be viewed through touch screen 120. Graphic elements displayed on the display 110 in display area 111 are selected, indicated, or manipulated by touching a corresponding location on touch screen 120. Touch screen 120 includes a first transparent substrate 122 with first transparent electrodes 130 formed in the x dimension on first transparent substrate 122 and a second transparent substrate 126 with second transparent electrodes 132 formed in the y dimension facing the x-dimension first transparent electrodes 130 on second transparent substrate 126. A dielectric layer 124 is located between first and second transparent substrates 122, 126 and first and second transparent electrodes 130, 132. Referring also to the prior-art plan view of FIG. 11, in this example first pad areas 128 in first transparent electrodes 130 are located adjacent to second pad areas 129 in second transparent electrodes 132 in display area 111. (First and second pad areas 128, 129 are separated into different parallel planes by dielectric layer 124.) First and second transparent electrodes 130, 132 have a variable width and extend in orthogonal directions (for example as shown in U.S. Patent Application Publication Nos. 2011/0289771 and 2011/0099805). When a voltage is applied across first and second transparent electrodes 130, 132, electric fields are formed between first pad areas 128 of x-dimension first transparent electrodes 130 and second pad areas 129 of y-dimension second transparent electrodes 132.
A display controller 142 (FIG. 10) connected through electrical busses 136 controls display 110 in cooperation with a touch-screen controller 140. Touch-screen controller 140 is connected through electrical busses 136 and wires 134 outside display area 111 and controls touch screen 120. Touch-screen controller 140 detects touches on touch screen 120 by sequentially electrically energizing and testing x-dimension first and y-dimension second transparent electrodes 130, 132.
Referring to FIG. 12, in another prior-art embodiment, rectangular first and second transparent electrodes 130, 132 are arranged orthogonally in display area 111 projected from display 110 onto first and second transparent substrates 122, 126 with intervening transparent dielectric layer 124, forming touch screen 120 which, in combination with display 110 forms touch screen and display system 100. First and second pad areas 128, 129 are formed where first and second transparent electrodes 130, 132 overlap. Touch screen 120 and display 110 are controlled by touch screen and display controllers 140, 142, respectively, through electrical busses 136 and wires 134 outside display area 111.
The electrical busses 136 and wires 134 are electrically connected to first or second transparent electrodes 130, 132 but are located outside display area 111. However, at least a portion of electrical busses 136 or wires 134 are formed on touch screen 120 to provide the electrical connection to first or second transparent electrode 130, 132. It is desirable to increase the size of display area 111 with respect to the entire display 110 and touch screen 120. Thus, it can be helpful to reduce the size of wires 134 and busses 136 in touch screen 120 outside display area 111. At the same time, to provide excellent electrical performance, wires 134 and busses 136 need a low resistance. Furthermore, to reduce manufacturing costs, it is desirable to reduce the number of manufacturing steps and materials in touch screen 120.
Touch-screens including very fine patterns of conductive elements, such as metal wires or conductive traces, are known. For example, U.S. Patent Application Publication No. 2010/0026664 teaches a capacitive touch screen with a mesh electrode, as does U.S. Pat. No. 8,179,381. Referring to FIG. 13, a prior-art x- or y-dimension variable-width first or second transparent electrode 130, 132 includes a micro-pattern 156 of micro-wires 150 arranged in a rectangular grid. The micro-wires 150 are multiple very thin metal conductive traces or wires formed on the first and second transparent substrates 122, 126 (not shown in FIG. 13) to form the x- or y-dimension first or second transparent electrodes 130, 132. The micro-wires 150 are so narrow that they are not readily visible to a human observer, for example 1 to 10 microns wide. The micro-wires 150 are typically opaque and spaced apart, for example by 50 to 500 microns, so that the first or second transparent electrodes 130, 132 appear to be transparent and the micro-wires 150 are not distinguished by an observer.
U.S. Patent Application Publication No. 2011/0291966 discloses an array of diamond-shaped micro-wire structures. In this disclosure, a first electrode includes a plurality of first conductor lines inclined at a predetermined angle in clockwise and counterclockwise directions with respect to a first direction and provided at a predetermined interval to form a grid-shaped pattern. A second electrode includes a plurality of second conductor lines, inclined at the predetermined angle in clockwise and counterclockwise directions with respect to a second direction, the second direction perpendicular to the first direction and provided at the predetermined interval to form a grid-shaped pattern. This arrangement is used to inhibit Moiré patterns. The electrodes are used in a touch screen device. Referring to FIG. 14, this prior-art design includes micro-wires 150 arranged in a micro-pattern 156 with the micro-wires 150 oriented at an angle to the direction of horizontal first transparent electrodes 130 in a first layer (e.g. first transparent substrate 122 in FIG. 12) and vertical second transparent electrodes 132 in a second layer (e.g. second transparent substrate 126 in FIG. 12).
A variety of layout patterns are known for micro-wires used in transparent electrodes. U.S. Patent Application Publication No. 2012/0031746 discloses a number of micro-wire electrode patterns, including regular and irregular arrangements. The conductive pattern of micro-wires in a touch screen can be formed by closed figures distributed continuously in an area of 30% or more, preferably 70% or more, and more preferably 90% or more of an overall area of the substrate and can have a shape where a ratio of standard deviation for an average value of areas of the closed figures (a ratio of area distribution) can be 2% or more. As a result, a Moiré phenomenon can be prevented and excellent electric conductivity and optical properties can be satisfied. U.S. Patent Application Publication No. 2012/0162116 discloses a variety of micro-wire patterns configured to reduce or limit interference patterns. As illustrated in prior-art FIG. 15, U.S. Patent Application Publication No. 2011/0007011 teaches a first or second transparent micro-wire electrode 130, 132 having micro-wires 150 arranged in a micro-wire pattern 156.
However, as noted above, it is useful to form electrical busses 136 and wires 134 with a reduced size compared to transparent micro-wire electrodes outside display area 111 in touch screen 120. To provide excellent electrical performance, wires 134 and electrical busses 136 need a low resistance. It is also desirable to reduce the number of manufacturing steps and materials in touch screen 120. There is a need, therefore, for an improved electrically conductive structure that is compatible with transparent electrodes, provides improved conductivity, and is robust in the presence of faults.